U.S. patent number 10,513,436 [Application Number 15/375,692] was granted by the patent office on 2019-12-24 for production of pure hydrogen and synthesis gas or carbon with cuo-fe2o3 oxygen carriers using chemical looping combustion and methane decomposition/reforming.
This patent grant is currently assigned to U.S. Department of Energy. The grantee listed for this patent is United States Department of Energy. Invention is credited to Ranjani Siriwardane, Hanjing Tian.
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United States Patent |
10,513,436 |
Siriwardane , et
al. |
December 24, 2019 |
Production of pure hydrogen and synthesis gas or carbon with
CUO-Fe2O3 oxygen carriers using chemical looping combustion and
methane decomposition/reforming
Abstract
Methods, systems and apparatus relate to producing synthesis gas
or carbon and hydrogen utilizing a reduced catalyst
CuO--Fe.sub.2O.sub.3. The method comprises introducing CH.sub.4;
reducing the CuO--Fe.sub.2O.sub.3 with the introduced CH.sub.4,
yielding at least a reduced metal catalyst; oxidizing the reduced
metal with O.sub.2 yielding CuO--Fe.sub.2O.sub.3; and generating
heat that would be used for the hydrogen and carbon or syngas
production with the reduced catalyst CuO--Fe.sub.2O.sub.3.
Inventors: |
Siriwardane; Ranjani
(Morgantown, WV), Tian; Hanjing (Morgantown, WV) |
Applicant: |
Name |
City |
State |
Country |
Type |
United States Department of Energy |
Washington |
DC |
US |
|
|
Assignee: |
U.S. Department of Energy
(Washington, DC)
|
Family
ID: |
68979565 |
Appl.
No.: |
15/375,692 |
Filed: |
December 12, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
62265677 |
Dec 10, 2015 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01J
23/745 (20130101); B01J 37/16 (20130101); C01B
3/26 (20130101); C01B 3/40 (20130101); C01B
3/382 (20130101); C01B 3/06 (20130101); B01J
37/18 (20130101); C01B 3/24 (20130101); C01B
2203/02 (20130101); C01B 2203/0261 (20130101); C01B
2203/1076 (20130101); C01B 2203/0475 (20130101); Y02P
20/52 (20151101); C01B 2203/0277 (20130101); C01B
2203/0233 (20130101); Y02E 60/36 (20130101); C01B
2203/1047 (20130101); C01B 2203/1241 (20130101); C01B
2203/0838 (20130101) |
Current International
Class: |
B01J
23/745 (20060101); C01B 3/24 (20060101); C01B
3/06 (20060101); C01B 3/40 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Orlando; Amber R
Assistant Examiner: Iqbal; Syed T
Attorney, Agent or Firm: Harney; Timothy L. Dobbs; Michael
J. Lally; Brian J.
Government Interests
STATEMENT OF GOVERNMENT SUPPORT
The United States Government has rights in this invention pursuant
to an employer/employee relationship between the inventors and the
U.S. Department of Energy, operators of the National Energy
Technology Laboratory (NETL).
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This non-provisional patent application is related to and claims
priority from U.S. Provisional Patent Application No. 62/265,677
filed Dec. 10, 2015, the complete subject matter of which is
incorporated herein by reference.
Claims
We claim:
1. A method for producing synthesis gas or carbon and hydrogen
utilizing a reduced CuO--Fe.sub.2O.sub.3 oxygen carrier, the method
comprising: introducing CH.sub.4 to the CuO--Fe2O3 oxygen carrier;
reducing the CuO--Fe.sub.2O.sub.3 oxygen carrier with the
introduced CH.sub.4, yielding at least a reduced oxygen carrier;
introducing methane to a first portion of the reduced oxygen
carrier, producing carbon and hydrogen by methane decomposition,
wherein the reduced oxygen carrier acts as a catalyst for methane
decomposition; introducing steam to the first portion for the
gasification of the carbon, thereby producing syngas; and oxidizing
a second portion of the reduced oxygen carrier with O.sub.2
yielding CuO--Fe.sub.2O.sub.3; and generating heat from the
oxidation reaction, wherein the heat is applied to the gasification
reaction and the methane decomposition reaction.
2. The method of claim 1, further comprising reducing the
CuO--Fe.sub.2O.sub.3 with the introduced CH.sub.4, yielding
CO.sub.2 and H.sub.2O in addition to the reduced oxygen carrier,
wherein the CO.sub.2 is sequestration ready.
3. The method of claim 2, further comprising decomposing the
CH.sub.4, yielding C and 2H.sub.2.
4. The method of claim 3, further comprising gasifying the yielded
C with steam, yielding CO and H.sub.2.
5. The method of claim 1, further comprising steam reforming the
CH.sub.4 using the reduced oxygen carrier as a steam reforming
catalyst.
6. The method in claim 1, further comprising producing a
concentrated CO.sub.2 stream that is sequestration ready from the
reduction of the oxygen carrier.
7. A method for producing synthesis gas or carbon and hydrogen, the
method comprising: reducing a CuO--Fe.sub.2O.sub.3 oxygen carrier,
yielding at least a reduced oxygen carrier and CO.sub.2, wherein
the CO.sub.2 is sequestration ready; introducing methane; producing
carbon and hydrogen with the reduced oxygen carrier, wherein the
reduced oxygen carrier acts as a catalyst for methane
decomposition; introducing steam to generate syngas by carbon
gasification; and generating heat by oxidation of the reduced
oxygen carrier, wherein the heat is applied to the methane
decomposition reaction and the gasification reaction.
8. The method of claim 7, further comprising reducing the
CuO--Fe.sub.2O.sub.3 with CH.sub.4, yielding CO.sub.2 and H.sub.2O
in addition to the reduced oxygen carrier.
9. The method of claim 8, further comprising decomposing the
CH.sub.4, yielding C and 2H.sub.2.
10. The method of claim 9, further comprising gasifying the yielded
C with steam, yielding CO and H.sub.2.
11. The method of claim 7, further comprising reforming an
introduced CH.sub.4 using the reduced oxygen carrier and steam,
wherein the reduced oxygen carrier acts as a steam reforming
catalyst.
Description
BACKGROUND OF THE INVENTION
Capturing CO.sub.2 from power plants that use fossil fuels is one
of several strategies to reduce global CO.sub.2 emissions. The task
of removing CO.sub.2 from power plant flue gas is challenging
because existing methods for separate CO.sub.2 from the gas mixture
requires a significant portion of power plant output. The
separation task can be simplified by replacing conventional air
with pure oxygen so that the combustion products are just CO.sub.2
and water, which may be easily separated by condensation. However,
current commercial techniques for producing oxygen from air require
very energy-intense cryogenic processes. Chemical looping
combustion (CLC) is a novel combustion technology that utilizes an
oxygen carrier, such as metal oxide, to transport oxygen from air
to fuel, thereby avoiding direct contact between fuel and air. The
significant advantage of CLC over conventional combustion is that
CLC can produce a sequestration-ready CO.sub.2 stream--not diluted
by nitrogen (N2)--without expending any major energy required for
the separation of CO.sub.2. The overall CLC process, in which the
metal oxide cycles between oxidized and reduced states, is
exothermic. Several single metal oxides and bi-metallic oxides have
been reported in the literature as oxygen carriers a promising
bi-metallic oxygen carrier containing CuO and Fe.sub.2O.sub.3 for
both methane and coal CLC.
Production of hydrogen from methane has received much attention
because it is a promising energy source that is also
environmentally benign. Hydrogen is used in oil refineries, for
ammonia, methanol production, and fuel cells. Steam methane
reforming (SMR) is currently the most popular commercial method of
producing hydrogen. Synthesis gas produced in SMR must be further
processed in the water-gas shift reactor to produce a gas stream
containing H.sub.2 and CO.sub.2. An additional step is required to
separate CO.sub.2 and H.sub.2 to produce pure H.sub.2 and
sequestration ready CO.sub.2. The energy for the SMR process is
provided via methane combustion in air which produces a CO.sub.2
stream diluted with nitrogen and will require separation prior to
sequestration.
Various researchers have reported on the production of hydrogen and
synthesis gas using the chemical looping methane reforming process.
Methane partial oxidation using an oxygen carrier is one of the
processes reported for the production of synthesis gas. In this
process, an oxygen carrier is used directly in the fuel reactor to
partially oxidize hydrocarbons. Another process reported in the
literature for hydrogen production via CLC includes initial
reduction of the oxygen carrier with fuel, such as methane or
synthesis gas, followed by steam oxidation to produce hydrogen via
water splitting. A combination of partial oxidation with oxygen
carriers and hydrogen production via water splitting on the reduced
oxygen carrier is also reported. Other approaches reported include
integration of a traditional hydrocarbon steam reformer with the
CLC process, and a five step process to produce synthesis gas from
the CLC process using NiO as the oxygen carrier and the reduced
carrier as the steam reforming catalyst. The processes described in
this disclosure use neither partial oxidation of methane nor
hydrogen production via water splitting using steam oxidation.
Thermo-catalytic decomposition of methane to carbon and hydrogen
has received attention because the process produces hydrogen
directly without any additional gas processing. A recent systems
analysis indicated that the cost of hydrogen production by thermal
decomposition of methane is lower than the cost for the steam
reforming process. Catalysts containing nickel and iron have been
widely used for methane decomposition tests. In addition, carbon
formed in the methane decomposition process has also a commercial
value. This disclosure describes a process for producing hydrogen
and carbon by methane decomposition on copper oxide-iron oxide
catalysts coupled with methane CLC using a CuO--Fe.sub.2O.sub.3
oxygen carrier. This CuO--Fe.sub.2O.sub.3 is used as the oxygen
carrier for the chemical looping process while the reduced CuO--
Fe.sub.2O.sub.3 carrier is used for the catalytic decomposition
process to produce hydrogen. The process produces a pure hydrogen
stream and carbon along with a sequestration-ready CO.sub.2 stream.
In addition to pure hydrogen, steam gasification of carbon formed
during methane decomposition produces a synthesis gas stream with
the ratio of H.sub.2/CO of 2, which is suitable for chemical
production.
The second process described in this paper occurs after the CLC
process with the CuO--Fe.sub.2O.sub.3 oxygen carrier. The reduced
oxygen carrier is used directly for the SM R process to produce
synthesis gas, similar to the commercial steam reforming process
with nickel-based catalysts. However, the heat required for the SMR
process is supplied by the CLC reaction with the oxygen carrier.
Syngas has many commercial applications: it can be used in the
Fisher-Tropsch process to produce diesel, or converted into other
useful chemicals such as methanol and dimethyl ether. Methanol is
used as the feedstock for production of formaldehyde, acetic acid,
propylene, and various esters, which are the chemical building
blocks in the production of plastics, resins, pharmaceuticals,
adhesives, paints, and much more. Nickel-based catalysts are
traditionally used in the commercial steam reforming process and
noble metal catalysts have also been reported. The reduced form of
the CuO--Fe.sub.2O.sub.3 catalyst is environmentally benign unlike
nickel catalysts, and the cost of the reduced CuO--Fe.sub.2O.sub.3
catalysts is significantly lower than noble metal catalysts used in
steam reforming processes.
SUMMARY
This invention serves to address the need for improved production
of synthesis gas and/or carb and hydrogen using a reduced catalyst
CuO--Fe.sub.2O.sub.3.
One embodiment relates to a method for producing synthesis gas or
carbon and hydrogen utilizing a reduced catalyst
CuO--Fe.sub.2O.sub.3. The method comprises introducing CH.sub.4;
reducing the CuO--Fe.sub.2O.sub.3 with the introduced CH.sub.4,
yielding at least a reduced metal catalyst; oxidizing the reduced
metal with O.sub.2 yielding CuO--Fe.sub.2O.sub.3; and generating
heat that would be used for the hydrogen and carbon or syngas
production with the reduced catalyst CuO--Fe.sub.2O.sub.3.
Yet another embodiment relates to a method for producing synthesis
gas or carbon and hydrogen. The method comprises reducing a
CuO--Fe.sub.2O.sub.3 catalyst, yielding at least a reduced metal;
generating heat by oxidation that would be used for the hydrogen
and syngas or carbon production with the reduced catalyst
CuO--Fe.sub.2O.sub.3; and producing a concentrated CO.sub.2 stream
that is sequestration ready while producing H.sub.2 and
C/syngas.
In summary, the CuO--Fe.sub.2O.sub.3 oxygen carrier has a dual
function in the process. It is used in the methane reduction/air
oxidation CLC process to provide energy for the endothermic methane
decomposition process to produce hydrogen and elemental carbon or
syngas while producing a concentrated sequestration-ready CO.sub.2
stream. After reduction with methane, the reduced oxygen carrier
also serves as a catalyst for the methane decomposition process to
produce hydrogen and elemental carbon or syngas. The reduced oxygen
carrier an also serves as a catalyst for the SMR process to
directly form syngas.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other features, aspects, and advantages of the multiple
embodiments of the present invention will become better understood
with reference to the following description, appended claims, and
accompanied drawings where:
FIG. 1 illustrates a system and process for production of H.sub.2
and synthesis gas (Option 1);
FIG. 2 illustrates another system and process for production of
H.sub.2 and synthesis gas (Option 2);
FIG. 3 illustrates a system and process for production of H.sub.2
and synthesis gas (Option 3);
FIGS. 4a-4b illustrate graphs depicting CLC of Methane with Cu--Fe
oxygen carrier at 800.degree. C. including FIG. 4a illustrating a
graph depicting reduction of Cu--Fe carrier with methane and FIG.
4b illustrating a graph depicting oxidation of reduced Cu--Fe
carrier with air;
FIGS. 5a-5b illustrate graphs depicting Cycle 1 at 800.degree. C.
including FIG. 5a illustrating a graph depicting methane
decomposition to produce H.sub.2 and carbon gasification with steam
with reduced Cu--Fe carrier and FIG. 5b illustrating a graph
depicting oxidation of Cu--Fe carrier with air as in process;
FIGS. 6a-6b illustrate graphs depicting cycle 4 at 800.degree. C.
including FIG. 6a illustrating a graph depicting methane
decomposition to produce H.sub.2 and carbon gasification with steam
with reduced Cu--Fe carrier and FIG. 6b illustrating oxidation of
Cu--Fe carrier with air as in process;
FIG. 7 illustrates a graph depicting H.sub.2/CO composition during
the carbon gasification state at 800.degree. C.;
FIG. 8 illustrates a graph depicting comparison of the H.sub.2
production during the methane decomposition step at 700.degree. C.
and 800.degree. C.;
FIG. 9 illustrate a graph depicting comparison of the H.sub.2
concentration during carbon gasification step at 700.degree. C. and
800.degree. C.;
FIG. 10 illustrates a system and process (Process 2) for
reduction-steam reforming-oxidation;
FIG. 11 illustrates a graph depicting thermodynamic (heats of
reactions by Factsage 6.0) and analysis of reduction with methane
(CH.sub.4+4MeO.dbd.CO.sub.2+4Me+2H.sub.2O) and oxidation with steam
(Me+H.sub.2O.dbd.MeO+H.sub.2) as a function of various compositions
of CuO/Fe.sub.2O.sub.3;
FIG. 12a-12c illustrate graphs depicting bench-scale flow reactor
test data for process 2 including FIG. 12a illustrates a graph
depicting Outlet gas composition during methane steam reforming
with reduced CuO/Fe.sub.2O.sub.3-alumina oxygen carrier, FIG. 12b
illustrates a graph depicting H.sub.2/CO ratios during methane
steam reforming with reduced oxygen carrier, and FIG. 12c
illustrates a graph depicting oxidation with air (800.degree. C.
(cycle 3, 4 g catalyst, 20% methane/30% steam for reforming);
FIG. 13 illustrates a graph depicting bench-scale flow reactor test
data for process 2 during methane steam reforming cycle 3 with
reduced CuO--Fe.sub.2O.sub.3-alumina oxygen carrier at 800.degree.
C. with 10% methane/30% steam (reduction time .about.15 min
reforming for .about.400 min];
FIG. 14 illustrates a graph depicting comparison of syngas (cycle
3) with reduced CuO--Fe.sub.2O.sub.3-alumina and commercial
NiO/Al.sub.2O.sub.3 catalyst at 800.degree. C. with 20% methane/30%
steam;
FIG. 15 illustrates a graph depicting combined heats for CLC
reduction reaction 1, air oxidation by steam reaction 5 computed
for different compositions of the Cu/Fe ratios of the oxygen
carrier with final reduction states Cu.sup.0 and Fe.sup.0; and
FIG. 16 illustrates a graph depicting combined heats for the CLC
reduction reaction 1, air oxidation reaction 3 and oxidation by
steam reaction 5 computed for different compositions of the Cu/Fe
in the oxygen carrier with final reduction states Cu.sup.0 and
Fe.sup.0.
DETAILED DESCRIPTION OF THE INVENTION
Experimental
Bench-scale fixed-bed flow reactor tests were conducted to
demonstrate the two processes. The oxygen carrier contained 30 wt.
% CuO, 30 wt. % Fe.sub.2O.sub.3/Al.sub.2O.sub.3. The materials were
tested in a fixed-bed flow reactor with an inner diameter of 13 mm.
The CuO--Fe.sub.2O.sub.3 oxygen carrier (-4 g) was placed in the
reactor to obtain a solid material bed height of about 2 cm. The
particle size of CuO--Fe.sub.2O.sub.3 oxygen carrier is in the
range of 100-150 microns with an average of 130 microns, and
surface area was 12 m.sup.2/g. For Process 1, reaction gases were
20% CH.sub.4/He for the reduction/decomposition reaction; dry air
for oxidation and 30% H.sub.2O/He for carbon gasification were
introduced in down flow mode at a flow rate of 90 seem. A mass
spectrometer (Peffier) was utilized for gas analysis from the
outlet of the reactor. For Process 2, 20% CH.sub.4/30% H.sub.2O/He
were used during the steam reforming step.
Results and Discussion
Production of hydrogen from methane decomposition coupled with CLC
using CuO--Fe.sub.2O.sub.3 oxygen earner.
A method to produce pure hydrogen and carbon or syngas by catalytic
methane decomposition coupled with CLC process is described. One
unique feature in this process is that the oxygen carrier used for
the CLC process is also used as a catalyst for methane
decomposition after the initial reduction. Pure hydrogen maybe
generated during the methane decomposition step. Carbon, produced
from methane decomposition, may be used directly as a valuable
product or gasified by steam to produce synthesis gas, which is a
precursor for the production of many chemicals. Various reactor
system designs suitable for carbon removal from methane
decomposition can be applied in this process. If synthesis gas is
not necessary, it can be re-introduced as a fuel for initial
reduction of the oxygen carrier.
Three different options to produce pure hydrogen and synthesis gas
from methane are shown in FIGS. 1-3. In the first option (generally
designated 10 in FIG. 1), methane is introduced to the reactor 12
(reducer) for the reduction of the oxidized
CuO--Fe.sub.2O.sub.3/Al.sub.2O.sub.3 oxygen carrier to produce a
reduced carrier, CO.sub.2, and H.sub.2O reaction, as described in
following reaction: CuO--Fe.sub.2O.sub.3+CH.sub.4.fwdarw.Cu--Fe or
FeO+CO.sub.2+H.sub.2O (1)
When the oxygen carrier does not produce any CO.sub.2 or CO, but
rather starts to generate hydrogen, a portion of the reduced oxygen
carrier is transferred to reactor 14 in which methane decomposition
(reaction 2) takes place. CH.sub.4.fwdarw.C+2H.sub.2 (2)
The other portion of the reduced oxygen carrier is transferred to
reactor 16 (oxidizer) in which air is introduced for oxidation
(reaction 3). Cu--Fe or FeO+O2.fwdarw.CuO--Fe.sub.2O (3)
Since the methane decomposition reaction is endothermic, heat for
the reaction will be provided by the exothermic reaction 3 from the
oxidizer reactor 16. Carbon deposited on the oxygen carrier by
methane decomposition can be removed to obtain valuable carbon
products or it can be transferred to reactor 18 in which steam is
introduced to gasify the carbon to form synthesis gas (reaction 4)
18. C+H.sub.2O.fwdarw.CO+H.sub.2 (4)
The reduced metal oxide may also serve as a water-gas shift
catalyst to convert some carbon monoxide with water to produce
hydrogen and CO.sub.2. Then the carbon-free catalyst can be
re-introduced to reactor 14 to form hydrogen. The synthesis gas
produced from carbon in reactor 4 can be either used for
applications to produce valuable chemical products or reintroduced
as fuel for the CLC reducer, reactor 12.
FIG. 2 illustrates Option 2, generally designated 100, where
reactions 1 and 2 may also be performed in a single reactor 114
instead of two reactors (reactors 14 and 16 in FIG. 1) by switching
gas between methane and steam, as illustrated in FIG. 2. FIG. 3
illustrates Option 3, in which the process may also be performed in
a four-step sequence (including reactors 212, 214, 216 and 218) as
illustrated in FIG. 3 (Option 3). The individual steps in this
process with the CuO--Fe.sub.2O.sub.3/Al.sub.2O.sub.3 oxygen
carrier were experimentally evaluated.
Experimental Data for Production of Hydrogen from Methane
Decomposition Coupled with CLC Using a CuO--Fe.sub.2O.sub.3 Oxygen
Carrier
Two step reactions, reduction with methane and oxidation with air
at 800.degree. C., were conducted demonstrating the CLC reactions
with the oxygen carrier, and the results are illustrated in FIG. 4
(See FIGS. 4a-4B). Methane was fully combusted by the oxygen
carrier to form CO.sub.2 and water during reduction and was fully
oxidized during oxidation with air. This material has been tested
for 50 cycles in a fluidized bed reactor and stable reactivity was
observed. Attrition resistance of the material was also better than
that of the standard fluid catalytic cracking (FCC) catalyst
(ASTM-5757-95 jet attrition method) after the 50 cycle test. These
experimental data demonstrated that the CuO--Fe.sub.2O.sub.3 oxygen
carrier is suitable for the CLC reactions required for the process
with methane in reactor 12 (reducer) and oxidation with air in
reactor 18 (oxidizer).
Reactor tests were also conducted to demonstrate the four
stepsrequired for generating pure hydrogen and hydrogen/carbon
monoxide. After the initial reduction, methane flow was continued
for methane decomposition, and the data on methane decomposition to
form hydrogen and carbon are illustrated in FIGS. 5a-5b; complete
conversion of methane to produce pure hydrogen was observed during
this step. It should be appreciated that CO was not observed during
this step, indicating that the oxygen carrier in the reduced form
does not supply oxygen but only acts as a catalyst for the methane
decomposition reaction. To avoid undesirable pressure build up and
flow restrictions, the methane decomposition step was limited to 35
minutes in the fixed bed tests even though the reduced oxygen
carrier was still active for the complete methane decomposition
process to produce hydrogen. Various reactor system designs
suitable for carbon removal from methane decomposition have been
reported in the literature. After 35 minutes of pure hydrogen
production with 100% conversion of methane, steam was introduced to
the catalyst to gasify carbon formed during the reaction. Synthesis
gas was formed during steam gasification of elemental carbon at
800.degree. C. The steam gasification step was not difficult since
gasification involved elemental carbon that was deposited on the
surface of the reduced oxygen carrier. The results during steam
introduction are also shown in FIGS. 5a-5b. The oxygen carrier was
then oxidized with air; results for the oxidation step are also
shown in FIGS. 5a-5b (where FIG. 5a illustrates a graph depicting
methane decomposition to produce H.sub.2 and carbon gasification
with steam with reduced Cu--Fe carrier as outlet concentration %
versus reaction time in minutes and FIG. 5b illustrates a graph
depicting oxidation of Cu--Fe carrier with air as in process as
O.sub.2 outlet concentration % versus reaction time in
minutes).
This reaction sequence-reduction, methane decomposition to form
hydrogen, steam gasification of carbon and oxidation with air-was
conducted for four cycles and the results for the fourth cycle is
shown in FIG. 6a-6b (where FIG. 6a illustrates a graph depicting
methane decomposition to produce H.sub.2 and carbon gasification
with steam with reduced Cu--Fe carrier as outlet concentration %
versus reaction time in minutes and FIG. 6b illustrating oxidation
of Cu--Fe carrier with air as in process as O.sub.2 outlet
concentration % versus reaction time in minutes).
The results shown in FIGS. 5a-5b and 6a-6b indicated stable
performance during the cyclic tests. The summary of the four-cycle
tests at 800.degree. C. is shown in Table 1. Consistent performance
was observed during the cyclic tests, as shown in Table 1.
When this reaction sequence was conducted at 700.degree. C.,
hydrogen formation was observed during the methane decomposition
step and synthesis gas was formed during the carbon gasification
step with steam similar to what was observed at 800.degree. C.
However, methane was not fully consumed during the methane
decomposition step at 700.degree. C., as was observed at
800.degree. C.
Hydrogen/carbon monoxide ratios during carbon gasification with
steam at 800.degree. C. are shown in FIG. 7. The ratio remains
close to 2 during this step, which is a desirable hydrogen/carbon
monoxide ratio for further processing of synthesis gas to produce
chemicals, such as methanol or formaldehyde. Therefore, syngas
formed during carbon gasification can be used for production of
useful chemicals.
Comparative data on hydrogen production during the methane
decomposition step at 700.degree. C. and 800.degree. C. are shown
in FIG. 8. It is clear that conditions for producing pure hydrogen
are more favorable at 800.degree. C. At this temperature, the
hydrogen concentration from the methane decomposition reaction
remained same even after 30 minutes, but at 700.degree. C. the
hydrogen concentration decreased after 20 minutes. Lower reaction
rates of methane decomposition and lower initial reduction of the
oxygen carrier with methane at 700.degree. C. may have contributed
to the lower performance at 700.degree. C. compared to 800.degree.
C. Hydrogen concentrations during the steam gasification step at
800.degree. C. were similar to concentrations at 700.degree. C. as
shown in FIG. 9 indicating that the gasification reaction was
feasible even at a lower temperature.
Energy Analysis of the Process of Hydrogen Production from Methane
Decomposition Coupled with CLC Using a CuO--Fe.sub.2O.sub.3 Oxygen
Carrier
The four reactions-methane reduction, methane decomposition, and
carbon gasification and oxidation reactions-were combined into two
reaction schemes as follows:
Reaction scheme A: Methane decomposition and carbon gasification
CH.sub.4.dbd.C+2H.sub.2 C+H.sub.2O=CO+H2
CH.sub.4+H.sub.2O.fwdarw.CO+3H2 CH.sub.4+Metal
oxides=CO2+H.sub.2O+reduced metal (5) Reaction Scheme B: Reduced
metal+0.sub.2=Metal oxides CH.sub.4+20.sub.2=CO.sub.2+2H2O (6)
FIG. 1 depicts a schematic where the reduced CLC oxygen carrier is
also utilized as the catalyst for the two-step methane
decomposition/steam gasification reaction. In this process, the CLC
reaction provides energy to the two-step methane
decomposition/steam gasification process. The heat of reactions for
the two-step methane decomposition/steam gasification (reaction
5-scheme A) and the overall CLC process (reaction 6-scheme B) at
various temperatures are summarized in Table 2. Reaction scheme A
consists of two reactions: the first reaction is a coking reaction,
which is depicted as occurring in reactor 2 in FIG. 1. This
reaction results in pure hydrogen production. The second reaction
in scheme A is the oxidation of carbon deposited on the
carrier/catalyst surface (reactor 16 in FIG. 1) via steam oxidation
to produce synthesis gas. Both of these reactions are endothermic
requiring energy to be sustained. For example, 226.4 kJ (Table 2)
is required per a mole of methane at 800.degree. C. for two-step
methane decomposition/steam gasification (reaction 5-scheme A)
occurring in reactors 14 and 16 (FIG. 1). To provide the energy
required for two-step methane decomposition/steam gasification, CLC
is intimately integrated as heat source. The CLC process is shown
FIG. 1 occurring in reactors 12 and 18. The overall heat of the
reaction for the CLC process, shown as reaction B at 800.degree. C.
is -800.9 kJ per mole of oxygen (Table 2). The CLC process may also
provide heat for steam generation, which has been intimately
integrated here by providing indirect heat to reactor 14 and direct
steam for reactor 16. While the heat duty required to carry
two-step methane decomposition/steam gasification is similar to the
heat duty of a traditional SMR scheme, the addition of CLC provides
a sequestration ready high-purity CO.sub.2 stream. In a traditional
SMR process, combustion of methane is necessary to produce the heat
required for the endothermic SMR reaction that generates CO.sub.2,
which is not sequestration ready.
An additional energy savings is also realized in the proposed
two-step methane decomposition/steam gasification due to the
elimination of the water-gas shift reaction step to produce
hydrogen and the CO.sub.2 separation step. In a traditional
commercial SMR process, methane is reacted with steam directly in
the SMR reactor and then processed through a water-gas-shift
reactor to produce a hydrogen and CO.sub.2 stream. Additional
separation techniques must be implemented to separate the CO.sub.2
and create a high-purity hydrogen stream. In the proposed process,
hydrogen can be produced without any additional separation process.
The proposed process also produces synthesis gas, which can be used
for production of specialty chemicals.
Coupling reaction schemes A and B, 1 mole of oxygen from the CLC
process produces 2 moles of pure hydrogen and synthesis gas
containing 1 mole of hydrogen and 1 mole of carbon monoxide.
Synthesis gas composition can vary since the reduced Fe--Cu oxide
can also act as a water-gas shift catalyst that can convert some
carbon monoxide to hydrogen. In addition, partial oxidation of the
reduced catalyst by water can form additional hydrogen. Moles of
oxygen involved in the CLC reaction B to provide heat for the
endothermic methane decomposition and carbon gasification reactions
are also listed in Table 2. Our experiments determined the oxygen
transfer capacity of the CuO--Fe.sub.2O.sub.3 oxygen carrier to be
13 wt % at 800.degree. C. The weights of the CuO--Fe.sub.2O.sub.3
oxygen carrier necessary to produce 3 moles of hydrogen and one
mole of carbon monoxide from 2 moles of methane are also listed in
Table 2. To produce the same quantity of hydrogen (1M scf/day] that
is produced from a commercial SMR process in the chemical and oil
industry, the solid circulating rate of the process in the current
paper need only be 266 pounds of solid per hour or only 31.4 g of
oxygen carrier per liter of feedstock, which is significantly less
than the 5 kg per kg of feedstock used in commercial fluidized
catalytic cracking processes.
Therefore, designing a commercial-scale reactor system with solid
processing for the current proposed process will not be
difficult.
A techno-economic analysis reported in the literature showed that
hydrogen could be produced by thermal decomposition of methane at a
lower cost than with the commercial steam reforming process. In the
process described in this paper, methane decomposition to produce
hydrogen is also combined with both synthesis gas production and
CLC to produce sequestration-ready CO.sub.2 which will contribute
to even more cost savings than reported in the techno-economic
analysis, if CO.sub.2 sequestration is considered as part of the
process.
Production of Synthesis Gas Directly from Methane Steam Reforming
Coupled with CLC Using a CuO--Fe.sub.2O.sub.3 Oxygen Carrier
Methane steam reforming is a well-established process. Steam and
hydrocarbon enter the reactor as feedstock, and hydrogen and carbon
monoxide are generated at the end of the process. The process is
governed by reactions 5 and 7. CO+H.sub.2O.fwdarw.CO.sub.2+H.sub.2
.DELTA.H.sub.298.sup.m=-41.2 kJ/mol (7)
The steam re-forming step, where methane reacts with water to
produce carbon monoxide and hydrogen, is an endothermic process.
Thus, the process is usually maintained at approximately
850.degree. C. to obtain a desirable conversion. The second step is
known as the water-gas shift reaction where syngas reacts to
recover hydrogen if the desired product is hydrogen instead of
synthesis gas.
For direct steam reforming, usually either nickel or noble metals,
such as ruthenium, rhodium, palladium, iridium, platinum, are used
as the active metal in catalysts. Nickel is the preferred metal for
industrial steam reforming applications because of its activity,
availability, and low cost. Methane is activated on the nickel
surface. The resulting CHx species then reacts with OH species
(from H.sub.2O) adsorbed on the nickel or on the support to form
the synthesis gas. However, it should be noted that nickel is not
environmentally benign since it is a suspected carcinogen. The
nickel oxide catalyst is initiated by hydrogen reduction so that
the surface active site of metallic nickel could be exposed.
Moreover, the industrial reformer must contain a methane combustor
to provide heat for the endothermic reforming reaction. All these
processes which use air for methane combustion produce CO.sub.2
that is not sequestration ready. In the process described in this
paper, the CLC process produces sequestration ready CO.sub.2 using
a CuO--Fe.sub.2O.sub.3 oxygen carrier that provides heat for the
steam reforming of methane. The reduced CuO--Fe.sub.2O.sub.3 oxygen
carrier is also the catalyst for the methane reforming step.
Process Steps Involved in Production of Synthesis Gas Directly from
Methane Steam Reforming Coupled with CLC Using a
CuO--Fe.sub.2O.sub.3--Al.sub.2O.sub.3 Oxygen Carrier
The proposed process is shown in FIG. 10. The process, generally
designated 300, consists of three reactors, 310, 312, 314. In
reactor 310, oxygen carrier reduction occurs with methane, as in a
traditional CLC process. The reduced oxygen carrier is then
transferred to a steam reformer 312 in step 2. Then the reduced
oxygen carrier acts as a steam reforming catalyst to produce
synthesis gas according to the reaction (5). Depending on the steam
content, the reduced oxygen carrier catalyst may also promote a
water-gas shift reaction (7) to convert some carbon monoxide to
hydrogen. In addition to acting as a catalyst, the fully reduced
oxygen carrier also gets partially oxidized by steam during the
steam reforming process.
Cu--Fe+H.sub.2O.fwdarw.CuO--FeO/Fe.sub.3O.sub.4/Fe.sub.2O.sub.3+H2
(8) The heats of the reaction used for steam reduction and
oxidation as a function of the Cu to Fe ratio are shown in FIG. 11.
When the Cu content is high, the reduction reaction is exothermic,
and oxidation with water is endothermic. When the Fe content is
high, the reduction reaction is endothermic, and the steam
oxidation reaction is exothermic. For the illustrated process, heat
from the CLC oxidation reaction (reactor 314] must be supplied for
either the reduction reactor (reactor 310) or the methane steam
reformer (reactor 312), depending on the composition of the oxygen
carrier. When the copper content is high, heat from reaction 314
for CLC air oxidation must be used for steam reforming reaction 5,
since steam oxidation reaction 8 is endothermic and the CLC
reduction reaction 310 is exothermic. When the iron content is
high, heat for air oxidation will be used mainly for CLC reduction
reaction 1 since the majority of the heat required for the steam
reforming reaction 5 can be provided by the steam oxidation
reaction 8, which is exothermic.
Experimental Data Involved in Producing Synthesis Gas Directly from
Methane Steam Using CuO--Fe.sub.2O/Al.sub.2O.sub.3 Oxygen
Carrier/Catalyst
The process was experimentally verified in the bench-scale reactor.
The initial reduction of the oxygen carrier (4 g) was performed
with 20% CH.sub.4/He for 11 min. at 800 C, which corresponded to
15% oxygen transfer capacity and possible oxidation states of
Cu.sup.0 and Fe.sup.0 Then, the methane steam reforming reaction
step 2 was performed with 20% CH.sub.4/30% H.sub.2O/He at
800.degree. C. for 120 mins; the results are shown in FIG. 12.
Oxidation was then performed at 800.degree. C. for 16 min with air,
also shown in FIG. 12. Oxidation time was 16 min, which
corresponded to 11% oxygen transfer indicating that the reduced
oxygen carrier was also partially oxidized by steam during the
steam reforming step in which steam supplied 4% of the oxygen
foroxidation.
The synthesis gas compositions at a lower methane to stream ratio
(10% methane and 30% steam) for this reaction sequence at
800.degree. C. are shown in FIG. 13. After reducing the oxygen
carrier for 15 minutes, methane steam was performed for 400 min.
The H.sub.2/CO ratio with 10% methane was about 2.5-3, which was
lower than that with 20% methane. When the steam preforming time
was 400 mins, the reduced oxygen carrier was fully oxidized with
steam, and it was not necessary to oxidize with air. When the
steam/methane content was high, the concentration of hydrogen
produced was higher. The desired synthesis gas composition can be
achieved by varying the concentration ratio of steam to
methane.
For comparison, 12% NiO/Al.sub.2O.sub.3, a commercial steam
reforming catalyst, and reduced
CuO--Fe.sub.2O.sub.3/Al.sub.2O.sub.3 were tested for the reaction
sequence under identical conditions (800.degree. C., 20% methane,
30%/o steam) and the results are shown in FIG. 14. During the steam
reforming step, H.sub.2/CO ratios for the
CuO--Fe.sub.2O.sub.3/Al.sub.2O.sub.3 oxygen carrier and the nickel
catalyst were similar but the 12% Ni/alumina commercial catalyst
had unconverted methane while CuO--Fe.sub.2O.sub.3/Al.sub.2O.sub.3
had fully converted methane.
Energy Analysis of the Production Process of Synthesis Gas from
Methane Steam Reforming Coupled with CLC Using CuO--Fe:zO 3 Oxygen
Carrier
The reduced oxygen carrier acts as a steam reforming catalyst to
produce synthesis gas according to reaction 5, which is
endothermic. In addition to acting as a catalyst, the fully reduced
oxygen carrier is also oxidized by steam during the steam reforming
process, which could be exothermic or endothermic depending on the
Cu to Fe ratio in the oxygen carrier as shown in FIG. 11. The CLC
reduction reaction 1 with methane can also be either endothermic or
exothermic depending on the Cu to Fe ratio of the oxygen carrier,
also shown in FIG. 11.
The oxidation reaction 3 with air is exothermic with the oxygen
carrier. Combined heats for reactions 1, 3, and 5 computed for
different compositions of the Cu/Fe in the oxygen carrier, are
shown in FIG. 15 using final reduction states of CuO and
Fe.sub.2O.sub.3 as Cu.sup.0 and Fe.sup.0, and the combined heats
using final reduction states of CuO and Fe.sub.2O.sub.3 as Cu.sup.0
and Fe.sup.0 are shown in FIG. 16. Amounts of solid material
necessary to process I mole of methane for the steam reforming
process are also shown in FIGS. 15 and 16. If Fe.sub.2O.sub.3 is
reduced to Fe.sup.0, results indicate that when copper content
increases, the amount of oxygen carrier necessary for the process
also increases. However, the amount of oxygen carrier necessary for
the process decreases with increasing copper content when Fe.sub.2O
reduction is limited to Fe.sup.0, as shown in FIG. 16.
In order to produce the same quantity of hydrogen (1M scf/day) that
is produced from a commercial SMR process in the chemical and oil
industry, the solid circulating rate of the process described in
this paper need only be 266 pounds of solid per hour or only 31.4 g
of oxygen carrier of per liter of feedstock, which is significantly
less than 5 kg per kg of feedstock used in the commercial fluidized
catalytic cracking process. Therefore, designing a commercial-scale
reactor system with solid processing for the current proposed
process will not be difficult.
CONCLUSIONS
Two processes to form pure hydrogen and synthesis gas from methane
coupled with CLC were evaluated using a
CuO--Fe.sub.2O.sub.3/Al.sub.2O.sub.3 oxygen carrier.
CuO--Fe.sub.2O.sub.3 was very effective as an oxygen carrier for
the reduction of methane and oxidation with air. In the first
process, the reduced oxygen carrier served as a catalyst for
methane decomposition to produce pure hydrogen and carbon. Carbon
deposited on the oxygen carrier was gasified with steam to produce
synthesis gas. After carbon was removed, it was re-used as a
catalyst for methane decomposition. Heat for the endothermic
methane decomposition and steam carbon gasification was provided by
the methane CLC reaction of the CuO--Fe.sub.2O.sub.3 oxygen
carrier. The process steps were evaluated in a bench-scale reactor
and performed consistently during cyclic tests. Performance was
better at 800.degree. C. than 700.degree. C. In the second process,
the reduced CuO--Fe.sub.2O.sub.3/Al.sub.2O.sub.3 oxygen.
Having described the basic concept of the embodiments, it will be
apparent to those skilled in the art that the foregoing detailed
disclosure is intended to be presented by way of example.
Accordingly, these terms should be interpreted as indicating that
insubstantial or inconsequential modifications or alterations and
various improvements of the subject matter described and claimed
are considered to be within the scope of the spirited embodiments
as recited in the appended claims. Additionally, the recited order
of the elements or sequences, or the use of numbers, letters or
other designations therefor, is not intended to limit the claimed
processes to any order except as may be specified. All ranges
disclosed herein also encompass any and all possible sub-ranges and
combinations of sub-ranges thereof. Any listed range is easily
recognized as sufficiently describing and enabling the same range
being broken down into at least equal halves, thirds, quarters,
fifths, tenths, etc. As a non-limiting example, each range
discussed herein can be readily broken down into a lower third,
middle third and upper third, etc. As will also be understood by
one skilled in the art all language such as up to, at least,
greater than, less than, and the like refer to ranges which are
subsequently broken down into sub-ranges as discussed above. As
utilized herein, the terms "about," "substantially," and other
similar terms are intended to have a broad meaning in conjunction
with the common and accepted usage by those having ordinary skill
in the art to which the subject matter of this disclosure pertains.
As utilized herein, the term "approximately equal to" shall carry
the meaning of being within 15, 10, 5, 4, 3, 2, or 1 percent of the
subject measurement, item, unit, or concentration, with preference
given to the percent variance. It should be understood by those of
skill in the art who review this disclosure that these terms are
intended to allow a description of certain features described and
claimed without restricting the scope of these features to the
exact numerical ranges provided. Accordingly, the embodiments are
limited only by the following claims and equivalents thereto. All
publications and patent documents cited in this application are
incorporated by reference in their entirety for all purposes to the
same extent as if each individual publication or patent document
were so individually denoted.
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